Chemical weathering and CO_2 consumption of a high-erosion-rate karstic river: a case study of the Sanchahe River, southwest China

The Sanchahe River in southwest China is a tributary of the Wujiang River and experiences high erosion rates. Geochemical analysis was conducted on Sanchahe River basin samples collected in the wet and dry seasons of 2014 in order to better understand local chemical weathering processes, anthropogenic influences, and associated CO2 consumption. The samples' total dissolved solid concentrations were found to be significantly higher than that of the global river average. Ca2+was the dominant cation in the samples and accounted for 64 % and73 % of the total cations in the dry and wet seasons,respectively. HCO3-and SO42-were the dominant anions,accounting for 92 % of the total anions. Stoichiometry analyses of the river waters suggested that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid. The chemical weathering rates of carbonate and silicate evaporites in the Sanchahe River basin were estimated to be approximately 109.2 and 11.0 t/(km2a), respectively, much higher than both the global mean values and the Wujiang River, a typical karstic river.The CO2 consumption by carbonate and silicate weathering are estimated to be 597.4 9 103 and 325.5 9 103mol/(km2a), which are much higher than corresponding values in the Wujiang River, indicating a high erosion rate in the Sanchahe River basin.

Combinatorial analysis on spatial information statistics for the karst water environment in Guiyang,China

The karst groundwater system is extremely vulnerable and easily contaminated by human activities.To understand the spatial distribution of contaminants in the groundwater of karst urban areas and contributors to the contamination,this paper employs the spatial information statistics analysis theory and method to analyze the karst groundwater environment in Guiyang City.Based on the karst ground water quality data detected in 61 detection points of the research area in the last three years,we made Kriging evaluation isoline map with some ions in the karst groundwater,such as SO4 2-,Fe 3+,Mn 2+and F -,analyzed and evaluated the spatial distribution,extension and variation of four types of ions on the basis of this isoline map.The results of the analysis show that the anomaly areas of SO4 2-,Fe 3+,Mn 2+,Fand other ions are mainly located in Baba’ao,Mawangmiao and Sanqiao in northwestern Gui- yang City as well as in its downtown area by reasons of the original non-point source pollution and the contamination caused by human activities(industrial and domestic pollution).

Enrichment characteristics and risk assessment of Hg in bird feathers from Caohai wetland in Guizhou Province,China

Based on the analysis of the enrichment characteristics of Hg and Me Hg in bird feathers from Caohai National Nature Reserve in Guizhou, the risks of Hg pollution to the birds from Caohai wetland have been evaluated. The total Hg content of bird feathers ranges from 40 to 5058 ng/g with an average of 924 ng/g. The content of Me Hg is significantly correlated with total Hg(r = 0.68,p<0.01), and the content are among 0.75 and 113 ng/g.The total Hg content in the birds feathers is significantly dependent on their feeding habits, which is mainly in accordance with the following rule: carnivorous birds [ omnivorous birds that are mainly carnivorous [ omnivorous birds that are mainly herbivorous.There are also differences in the Hg enrichment ability in the different parts of bird feathers, and the total Hg and Me Hg content in the wing feathers are significantly higher than that in the other parts of feathers. The bioaccumulation coefficients of aqueous Hg and Me Hg by bird feathers are 0.9×10~4–112.13×10~4(mean value is 20.47×10~4) and 0.47×10~4–70.4×10~4(mean value is 9.52×10~4),respectively. Although the whole Hg level in Caohai bird feathers is not too high, the Hg content in some carnivorous birds exceeds over or approaches the abnormal threshold when birds are breeding(5 μg/g), which indicates that the birds in Caohai wetland are faced with some risks of ecological Hg pollution.

Influence of Dry Density on Soil-Water Retention Curve of Unsaturated Soils and Its Mechanism Based on Mercury Intrusion Porosimetry

The soil-water retention curve(SWRC)can be used to evaluate the ability of unsaturated soils to attract water at various water contents and suctions. In this study, drying SWRCs for a kind of sandy soil were obtained in the laboratory by using self-modified SWRC apparatus. In addition, the porosity and the pore size distribution of the samples were investigated by a mercury porosimetry test in order to analyze the effect of dry density. Results showed that the soil-water retention of the soil specimens was strongly dependent on the dry density. Under zero suction, soil specimens with a higher dry density exhibited lower initial volumetric water content. The higher the dry density of soil, the more slowly the volumetric water content decreased with the increase of suction. There was a general and consistent trend for a soil specimen to possess a larger air-entry value and residual suction, while smaller slope of SWRC when it had a higher density. This was probably attributed to the presence of smaller interconnected pores in the soil specimen with a higher dry density. The proportion of large diameter pores decreased in comparison to pores with small diameters in the soil tested. The measured total pore volume of the soil specimen, which had a larger dry density, was lower than that of the relatively loose specimens.

A study on the adsorption of chromium on laterite from Guizhou Province,China

The adsorption behaviors of Cr(VI) on laterite from Guizhou Province were studied in this paper, and the adsorption mechanism was discussed as well. Results showed that different mineral compositions in the laterite would cause differences in the capacity of laterite to absorb Cr(VI). Gibbsite, iron oxide minerals and non-crystalloids are the main contributors to enhancing the capacity of laterite to absorb Cr(VI). The pH of the solution is an important factor affecting the adsorption of Cr(VI) on laterite. Acidic environment (pH=2-5) is favorable to the adsorption of Cr(VI). The amount of adsorbed Cr(VI) decreases with increasing pH of the solution. With increasing initial concentrations of Cr(VI), the amount of adsorbed Cr(VI) increases first, and then decreases. The optimal adsorption concentration of Cr(VI) on laterite is 250 μg/mL. The adsorption of Cr(VI) on laterite is a rapid process, about 80% Cr(VI) will be adsorbed within 2 hours. And the adsorption of Cr(VI) on kaolinite is a slow process.

The impact of sulfate reduction on the distribution of methylmercury in reservoirs in the city of Guiyang

In this paper, the relationship between sulfate reduction potential and mercury methylation potential was studied in the Aha, Baihua and Hongfeng reservoirs from Guiyang City. The methylmercury (MeHg) concentrations of lake water in the Aha Reservoir were greatly elevated as compared to those of the Hongfeng and Baihua reservoirs, which was correlated with its distinctly high SRB abundance, SO42-, and S2- concentrations. Among the three reservoirs, however, the highest MeHg was observed in in the top several centimenters of pore water profile in the Hongfeng Reservoir where the lowest S2- in pore water occurred. The distributions of MeHg in lake water and pore water showed the highest methylation potential occurred at water-sediment surface for the Aha Reservoir and the in the top several centimenters of sediments for the Hongfeng Reservoir. It is guessed that the highest mercury methylation only occurs at the sites with certain sulfide concentrations.

Landslide Susceptibility Mapping and Evaluation along a River Valley in China

Landslide susceptibility evaluation at regional scale is commonly performed based dominantly on the analysis of geological and geomorphological conditions of historical landslide cases. The main content of this type of evaluation covers identifying key casual factors, their critical groupings and relative importance. The present study demonstrates an application of the above concept to a 90 km long segment of Jinsbajiang River valley in China. Correlations of landslide occurrence with potential causative factors are derived according to interpretation of field investigation. Lithology, orientation of bedding planes, slope angle, stream action, rainfall and earthquake intensity are selectively recognized as identifiable/measurable causative factors to establish a factor domain. The membership grades, for field values of quantitative factors, to the susceptibility classes are determined based on the construction of fuzzy sets, while those for descriptive factors are assigned from a fuzzy score table. The analytic hierarchy process （AHP） is adopted for assigning weights to each individual factor. Subsequently, the evaluation is implemented in a GIS program IDRISI, where four classes of landslide susceptibility are identified and delineated in the subject area. The approach described in the present paper showed consistence with the nature and availability of data for evaluating landslide susceptibility at regional scale. The methodology presented can be effectively employed by relevant authorities to identify risky areas for dislocating major infrastructural project, and develop management strategies for land use.

Sodic metasomatism in a dacite weathering profile in Pinxiang, Guangxi, China

The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO*+Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase.

Effects of soil properties on production and bioaccumulation of methylmercury in rice paddies at a mercury mining area,China

Rice paddy soil is recognized as the hotspot of mercury（Hg） methylation, which is mainly a biotic process mediated by many abiotic factors. In this study, effects of key soil properties on the production and bioaccumulation of Hg and methylmercury（MeHg） in Hg-contaminated rice paddies were investigated. Rice and soil samples were collected from the active Hg smelting site and abandoned Hg mining sites（a total of 124 paddy fields） in the Wanshan Mercury Mine, China. Total Hg（THg） and MeHg in soils and rice grains, together with sulfur（S）,selenium（Se）, organic matter（OM）, nitrogen（N）, phosphorus（P）, mineral compositions（e.g., SiO2, Al2O3 and Fe2O3） and pH in soils were quantified. The results showed that long-term Hg mining activities had resulted in THg and MeHg contaminations in soil-rice system. The newly-deposited atmospheric Hg was more readily methylated relative to the native Hg already in soils, which could be responsible for the elevated MeHg levels in soils and rice grains around the active artificial Hg smelting site. The MeHg concentrations in soils and rice grains showed a significantly negative relationship with soil N/Hg, S/Hg and OM/Hg ratio possibly due to the formation of low-bioavailability Hg–S（N）–OM complexes in rhizosphere. The Hg–Se antagonism undoubtedly occurred in soil-rice system, while its role in bioaccumulation of MeHg in the MeHg-contaminated rice paddies was minor. However, other soil properties showed less influence on the production and bioaccumulation of MeHg in rice paddies located at the Wanshan Mercury Mine zone.

Additions to Pseudocamarosporium;two new species from Italy

Two coelomycetous taxa with muriform conidia were collected from Italy,and subjected to morpho-molecular taxonomic analyses.A mega blast search showed that the new taxa had a close relationship with Pseudocamarosporium.Maximum-likelihood and Bayesian analyses of combined LSU,SSU and ITS sequence data also showed that these strains reside in Didymosphaeriaceae and cluster with Pseudocamarosporium sensu stricto.Following detailed morphological and molecular analyses,these are introduced as new species in Pseudocamarosporium.The new taxa are illustrated and compared with other known species in the genus.

New macroalgal fossils of the Kaili Biota in Guizhou Province, China

The Kaili Biota of Jianhe County, Guizhou Province is found in a Burgess Shale type of deposits, and as such it provides a key fossil record for studying biotic differentiation following the Cambrian explosion. Macroalgae represent several important groups of primary producers and yet have not been well studied. Here, we report two new forms of macroalgae from the Kaili Biota, including a new genus and species and an indeterminate genus and species. The new genus and species, Parallelphyton tipica, is a heterotrichous alga with thalli composed of a prostrate cardinal axis, and parallel bundles of erect trichomes on the axis. The bifurcation of the trichomes is somewhat similar to the living heterotrichous Fritschiella (Chlorophyta), representing "architectonic differentiation" only known in higher plants as an adaptation to terrestrial conditions. The indeterminate genus and species consists of an arched, thick, cylindrical major shaft and irregularly spaced, curved lateral branches attached to the major shaft and subdivided into subbranches. The characteristics of the thick and strong major shaft and the lateral branch subdivided branches are analogous to the dichotomous branching of Psilophyton in Protopteridophyta. Thus, the differentiation of the thalli in these two algal forms represents the expression of properties of some higher metaphytes, indicating that the ecological differentiation of the macroalgae was well underway at the time of the Kaili Biota.

Effects of sulfate-reducing bacteria on methylmercury at the sediment–water interface

Sediment cores（containing sediment and overlying water） from Baihua Reservoir（SW China）were cultured under different redox conditions with different microbial activities, to understand the effects of sulfate-reducing bacteria（SRB） on mercury（Hg） methylation at sediment–water interfaces. Concentrations of dissolved methyl mercury（DMe Hg） in the overlying water of the control cores with bioactivity maintained（BAC） and cores with only sulfate-reducing bacteria inhibited（SRBI） and bacteria fully inhibited（BACI） were measured at the anaerobic stage followed by the aerobic stage. For the BAC and SRBI cores, DMe Hg concentrations in waters were much higher at the anaerobic stage than those at the aerobic stage, and they were negatively correlated to the dissolved oxygen concentrations（r =- 0.5311 and r =- 0.4977 for BAC and SRBI, respectively）. The water DMe Hg concentrations of the SRBI cores were 50% lower than those of the BAC cores, indicating that the SRB is of great importance in Hg methylation in sediment–water systems, but there should be other microbes such as iron-reducing bacteria and those containing specific gene cluster（hgc AB）, besides SRB,causing Hg methylation in the sediment–water system.